Generally, in order to manufacture semiconductor products, such as a semiconductor integrated circuit and so on, various processes, such as film forming processes, etching processes, oxidative diffusion processes, ashing processes, and modification processes, are repeatedly performed to, for example, a semiconductor wafer. From the standpoint of improving product yield, along with the high density growth and high miniaturization of semiconductor products, such various processes are required to further increase the evenness of the surface of the wafer to be processed, as well as to improve throughput in order to increase manufacturing efficiency.
Here, a single wafer process type plasma processing apparatus is explained as an example of a conventional processing apparatus. The plasma processing apparatus of this type is disclosed in, for example, patent documents 1 and 2 (listed below). FIG. 6 is an outline configuration diagram illustrating a conventional common plasma processing apparatus.
In FIG. 6, this plasma processing apparatus 2 has a process container 4 capable of vacuuming and a placing table 6 provided in the process container 4 for placing a semiconductor wafer W. And this placing table 6 is supported by a supporting arm 7 in a L-shape extending from the side wall of the container. On a ceiling section facing the placing table 6, a top plate 8, which transmits microwaves and is formed from aluminum nitride or quartz in a disk shape, is hermetically provided. And on the side wall of the process container 4, a gas nozzle 9 is provided to introduce a predetermined gas into the container.
And, on the surface of the top plate 8, provided are a disc-shaped planar antenna member 10 in a thickness of a few millimeters and a slow wave structure 12 consisting of, for example, a dielectric body, for shortening the wavelength of a microwave in the radius direction of the planar antenna member 10. Further, a plurality of microwave ejection holes 14 consisting of, for example slot-shaped through holes are formed. These microwave ejection holes 14 are generally arranged concentrically or spirally. And, a center conductor 18 of the coaxial wave guide 16 is connected on the center of the planar antenna member 10 and a microwave of 2.45 GHz, for example, generated from a microwave generator 20 is converted into a predetermined oscillation mode, and then guided through the center conductor 18. While the microwave is propagated to the radius direction of the antenna member 10 radially, the microwave is ejected from the microwave ejection holes 14 provided on the planar antenna member 10 and transmitted though the top plate 8. Next, the microwave is introduced into the process container 4 on the lower side, and a plasma is generated in the process space S in the process container 4 by this microwave.
Further, an exhaust opening 24 is provided on the bottom section 4A of the process container and an exhaust channel 32 in which a pressure control valve 26, first and second vacuum pumps 28 and 30 are inserted, is connected to this exhaust opening 24, thereby atmosphere in the process container 4 can be vacuumed. In such a configuration, a plasma is formed in the process space S in the process container 4 and the plasma process, such as plasma etching or plasma film forming, is applied to the semiconductor wafer W above.
By the way, when a predetermined process treatment is performed on a wafer, generally a predetermined gas is introduced into the process container 4 and the pressure in the process container 4 is controlled by the pressure control valve 26 as a preparation of performing this process treatment. When the pressure in the process container 4 is stabilized to the prescribed pressure, a predetermined process is performed by turning the plasma on.
Depending on the type of the process to the wafer, there is a case where a process is performed continuously by switching the gas types supplied to a single wafer. Such a process may be referred to as a so called multi-step process. In a case when performing such a multi-step process, the supply of a process gas is stopped when one process step is completed. Next, the residual gas in the process container 4 is exhausted once, and next, a procedure to stabilize the pressure is performed again by supplying a process gas for the next process. Thereafter, the step process is performed.    Patent document 1: Unexamined Japanese Patent Application Publication No. H9-181052.    Patent document 2: Unexamined Japanese Patent Application Publication No. 2002-311892.
By the way, in the process method described above, it certainly requires about 10 seconds to stabilize the pressure in the process container 4 due to the compressibility of the gas when performing the procedure of process treatment using the pressure control valve 26 (stabilization of the pressure), during which the process can not be executed, thereby resulting in a decrease of throughput.
Especially in a case of a multi-step process, because the exhaust process of the residual gas for a precedent process and the pressure stabilization process of the process gas for a subsequent process must be performed each time the gas type is switched, the throughput is significantly decreased.